6,477 research outputs found

    Exploring the Way to Approach the Efficiency Limit of Perovskite Solar Cells by Drift-Diffusion Model

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    Drift-diffusion model is an indispensable modeling tool to understand the carrier dynamics (transport, recombination, and collection) and simulate practical-efficiency of solar cells (SCs) through taking into account various carrier recombination losses existing in multilayered device structures. Exploring the way to predict and approach the SC efficiency limit by using the drift-diffusion model will enable us to gain more physical insights and design guidelines for emerging photovoltaics, particularly perovskite solar cells. Our work finds out that two procedures are the prerequisites for predicting and approaching the SC efficiency limit. Firstly, the intrinsic radiative recombination needs to be corrected after adopting optical designs which will significantly affect the open-circuit voltage at its Shockley-Queisser limit. Through considering a detailed balance between emission and absorption of semiconductor materials at the thermal equilibrium, and the Boltzmann statistics at the non-equilibrium, we offer a different approach to derive the accurate expression of intrinsic radiative recombination with the optical corrections for semiconductor materials. The new expression captures light trapping of the absorbed photons and angular restriction of the emitted photons simultaneously, which are ignored in the traditional Roosbroeck-Shockley expression. Secondly, the contact characteristics of the electrodes need to be carefully engineered to eliminate the charge accumulation and surface recombination at the electrodes. The selective contact or blocking layer incorporated nonselective contact that inhibits the surface recombination at the electrode is another important prerequisite. With the two procedures, the accurate prediction of efficiency limit and precise evaluation of efficiency degradation for perovskite solar cells are attainable by the drift-diffusion model.Comment: 32 pages, 11 figure

    Hyperbolic metamaterial as a tunable near-field spatial filter for the implementation of the active plasmon injection loss compensation scheme

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    We present how to physically realize the auxiliary source described in the recently introduced active plasmon injection loss compensation scheme for enhanced near-field superlensing. Particularly, we show that the characteristics of the auxiliary source described in the active plasmon injection scheme including tunable narrow-band and selective amplification via convolution can be realized by using a hyperbolic metamaterial functioning as a near-field spatial filter. Besides loss compensation, the proposed near-field spatial filter can be useful for real-time high resolution edge detection.Comment: 8 pages, 8 figure

    Rigorous numerical study of strong microwave photon-magnon coupling in all-dielectric magnetic multilayers

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    We demonstrate theoretically a strong local enhancement of the intensity of the in-plane microwave magnetic field in multilayered structures made from a magneto-insulating yttrium iron garnet (YIG) layer sandwiched between two non-magnetic layers with a high dielectric constant matching that of YIG. The enhancement is predicted for the excitation regime when the microwave magnetic field is induced inside the multilayer by the transducer of a stripline Broadband Ferromagnetic Resonance (BFMR) setup. By means of a rigorous numerical solution of the Landau-Lifshitz-Gilbert equation consistently with the Maxwell's equations, we investigate the magnetisation dynamics in the multilayer. We reveal a strong photon-magnon coupling, which manifests itself as anti-crossing of the ferromagnetic resonance (FMR) magnon mode supported by the YIG layer and the electromagnetic resonance mode supported by the whole multilayered structure. The frequency of the magnon mode depends on the external static magnetic field, which in our case is applied tangentially to the multilayer in the direction perpendicular to the microwave magnetic field induced by the stripline of the BFMR setup. The frequency of the electromagnetic mode is independent of the static magnetic field. Consequently, the predicted photon-magnon coupling is sensitive to the applied magnetic field and thus can be used in magnetically tuneable metamaterials based on simultaneously negative permittivity and permeability achievable thanks to the YIG layer. We also suggest that the predicted photon-magnon coupling may find applications in microwave quantum information systems

    Simulation of scattering from layered spheres with known surface electric field distributions using Mie theory and modified angular spectrum method: Applications to corneal sensing

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    Mie theory is a powerful method to evaluate the scattered fields from the multilayered sphere, where the incident field is expanded to the vector spherical harmonic (VSH) presentation. Then scattered fields are obtained by the T-matrix method. However, obtaining the VSH coefficients for arbitrarily shaped incident fields is difficult and time-consuming. This paper proposes a novel 3D angular spectrum method (3D ASM) for evaluating the VSH coefficients for the incident field, which is defined from the required electric field distribution positioned on the spherical surface. This allows the VSH expansion and evaluation of the scattered fields from a multilayered sphere illuminated with an arbitrary incident wavefront in the Mie Scattering range. This has been computationally challenging with previous methods. First, the advantage of the beam created with the proposed method compared to the nominal Gaussian beam illumination is addressed with the spherical bandstop filter simulation. Then the incident field computed by the proposed method is compared to the physical-optics simulations showing precise agreement. As an example of the proposed methodology, the cornea is modeled as a multilayered spherical structure, and the scattered fields are computed from the cornea illuminated by the incident field with spherical top-hat and tapered top-hat wavefronts. Also, the coupling coefficients of the incident and scattered fields from the cornea model are computed in the 200 - 400 GHz frequency range. The results are compared with coupling coefficients obtained with Gaussian beam illumination and referenced to the reflectivity obtained from plane wave illumination on an analog planar structure. The top-hat beams show increased agreement with the planar stratified medium theory compared to the plane wave and Gaussian beam illumination

    Phase retrieval of reflection and transmission coefficients from Kramers-Kronig relations

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    Analytic and passivity properties of reflection and transmission coefficients of thin-film multilayered stacks are investigated. Using a rigorous formalism based on the inverse Helmholtz operator, properties associated to causality principle and passivity are established when both temporal frequency and spatial wavevector are continued in the complex plane. This result extends the range of situations where the Kramers-Kronig relations can be used to deduce the phase from the intensity. In particular, it is rigorously shown that Kramers-Kronig relations for reflection and transmission coefficients remain valid at a fixed angle of incidence. Possibilities to exploit the new relationships are discussed.Comment: submitted for publicatio

    Near-Infrared Super Resolution Imaging with Metallic Nanoshell Particle Chain Array

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    We propose a near-infrared super resolution imaging system without a lens or a mirror but with an array of metallic nanoshell particle chain. The imaging array can plasmonically transfer the near-field components of dipole sources in the incoherent and coherent manners and the super resolution images can be reconstructed in the output plane. By tunning the parameters of the metallic nanoshell particle, the plasmon resonance band of the isolate nanoshell particle red-shifts to the near-infrared region. The near-infrared super resolution images are obtained subsequently. We calculate the field intensity distribution at the different planes of imaging process using the finite element method and find that the array has super resolution imaging capability at near-infrared wavelengths. We also show that the image formation highly depends on the coherence of the dipole sources and the image-array distance.Comment: 15 pages, 6 figure
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